Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.68 (tissue plasminogen activator)
 11,311 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Carboxy-terminal lysine residues on the surface of cells and fibrin bind plasminogen and control its activation. Since plasma contains basic carboxypeptidases, which remove carboxy-terminal lysines from protein substrates, we investigated if these enzymes are involved in the regulation of plasminogen binding sites. Plasma reduced plasminogen binding to cells, and this effect could be ascribed to the activity of the plasma carboxypeptidases. Purified carboxypeptidase N, which is constitutively active, and plasma carboxypeptidase B, which circulates as a zymogen, were both capable of significantly reducing plasminogen binding to cells. Dose titration experiments verified that plasma concentrations of either carboxypeptidase were sufficient to maximally affect plasminogen binding to cells. Furthermore, plasma carboxypeptidase B, but not carboxypeptidase N, reduced the rate of whole blood clot lysis induced by tissue-type plasminogen activator. These findings establish that plasma carboxypeptidases can modulate plasminogen binding to cells and control the rate of fibrinolysis. These functions delineate a novel role for the plasma carboxypeptidases in the regulation of the plasminogen system.
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PMID:Plasma carboxypeptidases as regulators of the plasminogen system. 759 93

The precursor of plasma carboxypeptidase B (pCPB) also known as thrombin-activable fibrinolysis inhibitor can be converted by thrombin to an active enzyme capable of eliminating C-terminal Lys- and Arg-residues from proteins. The activation is about 1000-fold more efficient in the presence of thrombomodulin (TM). We investigated the antifibrinolytic potency of maximally activated pCPB in plasma and explored the antifibrinolytic mechanism of pCPB. During clotting of plasma in the presence of 3.3 NIH units/ml thrombin and 1 microg/ml soluble TM, more than 80% pro-pCPB was converted into the active form causing an increase of plasma carboxypeptidase activity from 100 units/liter (constitutive activity ascribed to plasma carboxypeptidase N) to 430 units/liter as measured with furoylacroleyl-alanyl-arginine substrate. Under these conditions, lysis of a plasma clot induced by a range of tissue-type plasminogen activator (t-PA) concentrations (0.2-2 microg/ml) was retarded more than 4-fold. A considerable retardation of fibrinolysis was observed upon addition of as little as 12 ng/ml soluble TM, a concentration comparable with physiological concentrations of soluble TM in human plasma. The presence of Ca2+ appeared to be a critical requirement for effective activation of pro-pCPB by thrombin-TM in plasma. Plasminogen-binding sites (C-terminal lysines) on the surface of a plasmin-treated fibrin clot were eliminated within 1-3 min by plasma with maximally activated pCPB, as studied in a recently described model involving fluorescence microscopy. Confocal fluorescence microscopy showed that in the absence of TM plasminogen strongly accumulated on fibrin fibers during t-PA-induced lysis of a plasma clot. In the presence of TM (and a concomitant pro-pCPB activation), lysis was slow and was not accompanied by accumulation of plasminogen on the fibers. In conclusion, generation of active pCPB during clotting of plasma in the presence of Ca2+ and TM leads to a retardation of plasma clot lysis in a wide range of t-PA concentrations, from low to therapeutic, and to a fast elimination of plasminogen-binding sites on partially degraded fibrin. This is a likely mechanism for the antifibrinolytic effect of active pCPB.
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PMID:On the mechanism of the antifibrinolytic activity of plasma carboxypeptidase B. 916 90

Carboxypeptidase R (CPR) exists in precursor form (proCPR) in plasma in contrast to carboxypeptidase N (CPN), which is present in the active state. CPR plays two important roles, one of which appears to be the control of the inflammatory response by inactivation of anaphylatoxins such as complement-derived C3a and C5a. Therefore, an increase in CPR activity may facilitate rapid inactivation of these inflammatory mediators generated at the site of bacterial infection. Upregulation of proCPR expression during the inflammatory response initiated for instance by endotoxin (lipopolysaccharide) should play a role in suppressing hyper-reactivity as seen in septic shock. CPR also functions as an inhibitor of fibrinolysis, where its ability to prevent binding of plasminogen to lysine residues on fibrin clots significantly lengthens tissue plasminogen activator (tPA)-induced fibrinolysis time. Therefore, upregulation of proCPR production during the inflammatory response may exacerbate thrombosis contributing to the development of disseminated intravascular coagulation as well as other conditions involving thrombosis. Co-administration of tPA and a specific inhibitor of CPR, such as potato carboxypeptidase inhibitor, which does not affect CPN, may be useful in thrombolytic therapy.
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PMID:Carboxypeptidase R is an inactivator of complement-derived inflammatory peptides and an inhibitor of fibrinolysis. 1141 58

The Ca(2+)-dependent phospholipid-binding protein annexin II heterotetramer (AIIt) is composed of two copies of annexin II and a p11 dimer. The interaction of the carboxyl-terminal lysine residues of the p11 subunit of AIIt with the lysine-binding kringle domains of plasminogen is believed to play a key role in plasminogen binding and stimulation of the tPA-catalyzed cleavage of plasminogen to plasmin. In the current report, we show that AIIt-stimulated plasminogen activation is regulated by basic carboxypeptidases, in vitro. The incubation of AIIt with a 1/400 molar ratio of carboxypeptidase B for periods as short as 2 min resulted in a significant loss in AIIt-stimulated plasminogen activation. Carboxypeptidase B (CpB) as well as thrombin-activated fibrinolysis inhibitor (TAFIa) and carboxypeptidase N (CpN) rapidly reduced AIIt-stimulated plasminogen activation by 80%. The molar ratio of carboxypeptidase/AIIt for half-maximal inhibition of AIIt was 1/4700, 1/700, and 1/500 for CpB, TAFIa, and CpN, respectively. Treatment of AIIt with carboxypeptidase resulted in loss of both carboxyl-terminal lysine residues from the p11 subunit, which correlated with a decrease in the k(cat) and an increase in the K(m) for plasminogen activation. The data reveal a novel mechanism for the regulation of AIIt-stimulated plasminogen activation.
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PMID:The p11 subunit of annexin II heterotetramer is regulated by basic carboxypeptidase. 1193 91

A novel carboxypeptidase R (CPR) inhibitor, related to potato carboxypeptidase inhibitor (PCI), was designed using rational structure-based strategies, incorporating two principle facts: CPR has a strong affinity for basic amino acids, and the two lysine and arginine residues of PCI are orientated in the same direction and held in close spatial proximity by three disulfide bonds. Initially, a disulfide-bonded fragment of PCI was synthesized showing weak competitive inhibitory activity against CPR. Subsequently, a smaller linear 9-mer peptide, designated CPI-2KR, was designed/synthesized and found to be a more efficient competitive inhibitor of CPR, without affecting the activity of the other plasma carboxypeptidase, carboxypeptidase N. In vitro studies showed that, together with tissue plasminogen activator, CPI-2KR synergistically accelerated fibrinolysis, representing a lead compound for the design of smaller organic molecules for use in thrombolytic therapy.
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PMID:Rational structure-based design of a novel carboxypeptidase R inhibitor. 1240 97

A novel series of cyclic potent, selective, small molecule, thiol-based inhibitors of activated thrombin activatable fibrinolysis inhibitor (TAFIa) and the crystal structures of TAFIa inhibitors bound to porcine pancreatic carboxypeptidase B are described. Three series of cyclic arginine and lysine mimetic inhibitors vary significantly in their selectivity against other human basic carboxypeptidases, carboxypeptidase N and carboxypeptidase B. (-)2a displays TAFIa IC50 = 3 nM and 600-fold selectivity against CPN. Inhibition of TAFIa with (rac)2a resulted in dose dependent acceleration of human plasma clot lysis in vitro and was efficacious as an adjunct to tPA in an in vivo rabbit jugular vein thrombolysis model.
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PMID:3-Mercaptopropionic acids as efficacious inhibitors of activated thrombin activatable fibrinolysis inhibitor (TAFIa). 1718 88